Download and install Killdisk; alternatively, you can download a bootable image and burn a bootable CD with it.
Run Killdisk (or boot from the CD above) and make sure you select the correct drive you want to erase. Proceed to "kill" the disk - it will write zeroes all over it. When done, you may repeat the process again to make sure every trace of data was wiped. Then, format as needed using whatever utility you like for that.
Killdisk is easy to use, just make sure you select the correct drive, and also that you select the root of the drive - if it was partitioned before, it will show also the partitions, but you need to erase the whole drive. By doing that, you will also remove any prior partitioning information. Pretty much, the drive is restored in a factory-clean state.